The U.S. Department of Energy claims that the energy we use in an average house is responsible for twice as many greenhouse gas emissions as an average car. This is due to the fact that much of the energy we use in our buildings comes from fossil fuels. Therefore, any conservation action plan we implement should consider the building's cooling system as a major part of the efficiency solution. So how do we go about comparing these air conditioning units from an efficiency and cost-to-operate perspective?The standard measurement of energy efficiency for an air conditioner is SEER. This stands for Seasonal Energy Efficiency Ratio, and is an average of the cooling efficiency. In simple terms the higher the SEER, the more efficient the unit. For those of you gifted with an understanding of mathematics, here is the formula:
SEER = [Total Cooling Output Over the Cooling Season] / [Total Electrical Energy Input Over the Cooling Season]
If you find yourself wondering what's the SEER rating of my home or office AC, an easy way to determine what you have is to consider the approximate age of your air conditioning unit. If it is 10-15 years old it most likely has a SEER rating of about 6. That's because that was the highest rating available back then. If it's more than 15 years old, then consider yourself lucky that it's still running. The average lifespan of an AC is 15 years. You may want to consider investing the cost of servicing older units into a new more efficient one. In fact, as of January 23, 2006 the U.S. Department of Energy mandated a bare minimum SEER of 13. There is much more energy savings to be had with more efficient models. Today high efficiency units can reach a SEER rating of 27. To put this into perspective, if you replace a 13 SEER with a 27 SEER unit, you could save approximately 50% in energy use.
The SEER rating system was created to help you compare the operating costs of two or more units, giving you a better picture of your return on investment (ROI). So let’s look at an actual example in dollars and cents. We’ll use an average 3 ton or 36,000 btu unit that's commonly found in homes and estimate it will run an average of 8 hours a day. We'll run the numbers for 4 months at an average rate of $0.10 per kilowatt hour.
6 SEER (10-15 year old model)
36,000 BTU/hr x 976 hours / 6.0 SEER = 5,856,000 watts / 1,000 (to convert to KW) = 5,856 KW x $0.10 = $585.60 per year
13 SEER (Energy Efficient model)
36,000 BTU/hr x 976 hours / 13.0 SEER = 2,702,769 watts / 1,000 (to convert to KW) = 2,703 KW x $0.10 = $270.30 per year
In this case, replacing a 6 SEER with the minimum 13 SEER unit will save $315.30 per year. And switching to a high efficiency 27 SEER unit would save an additional $140.20 per year. Keep in mind, this example does not account for the greater savings of those in a “peak demand” pricing structure, which is commonly found throughout the southwest. In many cases, a new unit can reduce the peak load enough to get people out of the higher priced tiers. This example also shows only your savings at current utility rates. It doesn't reflect the additional savings with expected increases in energy costs over the next 15 years. Remember, a lower priced, less efficient model may offer a lower upfront cost, but you will pay much more for it over the course of its lifetime.
If you are considering replacing your unit, you may want to check with your local power company. Most of them offer ratepayer funded rebates to encourage the purchase of high SEER products that replace an existing lower SEER unit. Once the new system is installed, look to save even more energy and money by having your ducts tested. Typical houses lose about 20 percent of the air conditioned air in the duct system due to leaks, holes and poor connections. It would be a real shame to waste any of that wonderfully efficient cold air.
